The invention relates to communication units having a light guide for guiding light from a light source to illuminate a display. Light guides are also used to transfer light from a light source to illuminating the keyboard/keys. In mobile phones the light guide is placed between a printed circuit board and the display and/or the keyboard to transfer the light from a light source, e.g. a light emitting diode (LED), to illuminate the display or/and the keyboard.
This is e.g. shown in U.S. Pat. No. 5,746,493, where a light guide is described having a plurality of light coupling recesses. Some of the light coupling recesses are placed between keyholes on the light guide, where the LEDs mounted on a printed circuit board sticks up, and transfer through the light guide light for illuminating mainly the keyboard and partly the display. On one side of the light guide are the light coupling recesses arcuately shaped to transmit light from the LED uniformly into the light guide.
Another approach of illuminating a keyboard is shown is U.S. Pat. No. 5,711,588, where the light is reflected on a cover, mounted over the keys of a keyboard assembly, into the keys. In this case a light guide is not needed, nor is there a need for a light source for each key on the keyboard. Yet another approach is shown in U.S. Pat. No. 5,847,336, with one LED for each key to illuminate the keys directly. The LEDs are mounted on a flexible film, which is placed directly under the keyboard. Between this flexible film and the printed circuit board there is a dome sheet with domes that short-circuit a pair of electrical contacts on the printed circuit board, when pressing the keys. This approach is not used to illuminate the display, just the keyboard.
Still another approach is described in U.S. Pat. No. 5,708,428, where LEDs are embedded, by insert moulding, directly into the light guide. The light guide is placed between the keyboard and printed circuit board, having aperture for permitting the conductor on the bottom of each of the keys to contact respectively positioned contacts on the printed circuit board.
Furthermore, JP 9287981 describes a device for guiding the light from a substantially linear light-emitting element into a photo-conducting plate, without increasing the thickness of the plate. To manage to transmit the light without having a thicker plate a lens is used more exactly a Fresnel lens.
The invention provides a light guide for illuminating a display or a keyboard. The light guide is a substantially transparent plate-formed element with reception means for receiving light from light sources and for guiding the light into the transparent plate-formed element of the light guide. The reception means includes light in-coupling surfaces facing towards the light sources. The reception means is disposed in a plane that is in a substantially parallel relationship with the main surface of the light guide. The reception means includes a lens and a diffuser, for dispersing the light substantially parallel with the main surface of the light guide. The advantage provided by the light guide and associated lens and diffuser is that it allows for dispersing light in a light guide from LED""s in a printed circuit board (PCB) that is coupled to the light guide. The light can therefore be transferred efficiently without making the light guide too thick or too large.
The invention also provides a light guide for illuminating a display or a keyboard incorporated in a communication unit. This enables the communication unit to have an efficient transferring of light from a light source to a display or a keyboard without becoming too thick.
In another approach of the invention there is provided a plastic dome sheet placed on one side of the light guide. On the side, which is closest to the printed circuit board. The dome sheet includes a reflector sheet, which covers a part of the light guide that could be the back screen of the display.